This invention relates to a method and apparatus for zig-zag folding and, more particularly, constitutes an improvement over my prior U.S. Pat. No. 3,195,882. In that patent, to achieve higher speeds, the tip of the gripper anvil traced an envelope having a greater diameter than the envelope traced by the tucker. This represented a departure from the prior art which itself was improved by my prior U.S. Pat. No. 3,489,406. However, both of these patents deal with mechanically controlled grippers as contrasted to the resilient form of gripper of my U.S. Pat. No. 3,947,013.
The instant invention has to do with the first type of folding wherein the grippers are mechanically controlled. However, notwithstanding the precision ostensibly available from mechanically controlled grippers, it has become increasingly difficult to develop folds at precise locations, i.e., along spaced apart lines of transverse perforation--and, once so folded, there have been difficulties in separating a continuous stream of forms into exact count stacks.
It will be appreciated that a great demand exists for zig-zag folded forms for use in computers. Computers, particularly the print-out mechanisms, have been operating at ever-increasing speeds. Anything that interferes with the achievement of the higher speeds is, of course, undesirable and disadvantageous. One of these undesirable phenomena is that of stack "lean". By this, I refer to the fact that a free-standing stack, when viewed from the side and parallel to the fold lines assumes a parallelogram type of contour rather than the desired rectangle. This can be noted quickly during the process of manufacture but heretofore nothing has been done to correct this without stopping the machine.
I have ascertained that stack "lean " results from alternate forms or folds being longer than those intervening. The length of forms or folds normally is determined by the lines of transverse perforation existing in the sheet, and I have noted that in prior folders, the tucker and gripper about to enter into engagement "hunt" to seek the line of perforation, i.e., the weakest area in the portion of the web being folded. The difference in length between adjacent lines of peroration in adjacent forms may be only of the order of a few thousandths of an inch but it still results in the undesirable stack "lean".
I have ascertained that the undesirable "lean" which can disrupt the operation of the computer print mechanism by virtue of failing feed properly, can be overcome by a slight angular shift of one folding member relative to the other and this during operation so that the results thereof can be immediately ascertained.
Here it will be appreciated that there has been a demand for increasing speeds of production because there has been a shift to single part business forms--the ease and economy with which reeproduction can be made by xerographic type machines making it unnecessary to have multiple part forms. Thus, to maintain a given output of business forms, the forms manufacturer is desirous of operating at higher speeds which is reflected in differential tensions in the web which can result in slight mislocations in the lines of transverse perforation.
The problem of stack "lean" is substantially eliminated through the use of helical mating gears on the folding members whereby very slight angular adjustments can be made "on the fly". Such type of gearing has not been used, to the best of my knowledge, on folding rolls although such gearing has been used in adjusting the mating engagement of perforation rolls.
The instant invention also comprehends improvements in the zig-zag folding operation and apparatus other than merely eliminating stack "lean". When zig-zag folding is to be achieved at high speed, it is important to control the web carefully both before and after folding. In particular, the web fold in exiting from gripping engagement has to "drape" incident to being stacked. At high speeds, the draping or curving of the folded form can be subject to peculiar forces which may upset an entire stack, thereby destroying the utility of a considerable portion of a given production run. This advantageous control is achieved according to the instant invention through the structure and operation of the folding members to eliminate any surplus of paper upstream of the engaged gripping elements during tucking engagement thereof.
Still further, I provide a novel means and operation for controlling the drape incident to stacking and at the same time achieve a novel separation of the stack into constituents of exact count. More particularly, the invention provides a reliable and mechanical means and method for inserting a separator between the folds of a caged stack to burst the web bonds at a predetermined fold line.
Other objects and advantages of the invention may be seen in the details of the ensuing specification.